Within multiple-master, digital communication systems any station linked to the system may transmit data over a common communication bus at anytime. Invariably, within such systems, a monitoring and control arrangement must be provided to detect simultaneous data transmissions by multiple stations over the common communication bus, and terminate the colliding transmissions until the common bus is clear. While numerous data collision avoidance and detection arrangements exist for multiple-master, digital communication systems, typically they all include a listen-while-talking ("LWT") collision detection/avoidance scheme.
In a system employing an LWT scheme, each station monitors the common communication bus prior to transmitting, and if another transmission is determined to be already in progress, each monitoring station defers its transmission. Upon detecting that all other transmissions have ceased, and the common bus is clear, the station would then begin its own transmission while continuing to monitor the common bus (listening while talking). Unfortunately, one or more other stations which also deferred transmissions, and could begin transmitting at the moment the common bus clears. This would result in data collisions, which would be detected by all the transmitting stations (since each continues to monitor the common channel during transmission). Upon collision detection, each of the stations involved terminates transmission (referred to as "backing off") and enters into a contention to gain control of the bus. This contention is performed via digital processing according to a prescribed algorithm tailored to the particular multiple-master, digital communication system.
Another drawback of an LWT collision detection scheme is a window of collision which exists with respect to inter-station communications. A signal transmitted on a common bus by one station will not reach other stations linked to that bus for a finite interval (the transmission time between stations). One of the other stations linked to the common bus may erroneously commence transmitting a second signal on the bus during this interval as the bus would appear to be clear. This second signal would of course collide with the first signal. The actual window of collision for a given system is an interval of time equal to the maximum transmission time between stations within the system, plus the processing time required for any given station to recognize that the bus is clear and that it is the apparent winner of the contention for control of the bus. Since station contention within existing multimaster systems is performed via processing of complex software algorithms, the duration of the actual window of collision is usually many times greater than the maximum transmission time within the systems.